1. Field of the Invention
The present invention relates to a conveyor belt, a sheet feeding device including the conveyor belt, and an image forming apparatus including the sheet feeding device, such as, a copying machine, a printer, a facsimile machine, or other similar image forming apparatuses.
2. Discussion of the Background
An image forming apparatus such as, a copying machine, a printer, a facsimile machine, or other similar image forming apparatuses, uses a sheet feeding device that feeds original documents having images to be read by an image reading device to an image reading position and conveys the original documents toward an image forming device. The sheet feeding device has a sheet-through mechanism in which an original document is fed so as to pass over a stationary image reading device. An image of an original document, which has been conveyed onto a slit glass, is read by the stationary image reading device at the image reading position while moving the original document relatively to the image reading device.
In the sheet feeding device, several original documents out of a stack of original documents (hereafter referred to as “sheets”), which are stacked on an original document setting table, are picked up and fed by a sheet pick-up roller, and then fed one by one by a sheet feeding belt and a reverse roller provided downstream of the sheet pick-up roller in the sheet feeding direction. Then, the fed sheet is conveyed to the image reading position through a sheet conveying path in the sheet feeding device. A part of the sheet conveying path is formed between a conveyor belt and the slit glass, through which the fed sheet is conveyed to the image reading position. The conveyor belt is in a circular shape and spanned around a plurality of rollers.
In the above-described background sheet feeding device, the conveyor belt typically shifts in a direction perpendicular to the sheet conveying direction, that is, in the direction along the width of the belt, during rotation. To avoid a shift of the conveyor belt, a background sheet feeding device uses plates to regulate end portions of the conveyor belt in a direction perpendicular to the sheet conveying direction. In this background sheet feeding device, abrasion powder is typically produced between contact surfaces of the conveyor belt and the regulating plates. If abrasion powders scatter on a slit glass and a contact glass, spot and streak occur in the image of an original document read by an image reading device.
In another background sheet feeding device, a line of convex portions are provided on an inner circumferential surface of the conveyor belt in order to avoid shifting. The convex portions engage in concave portions formed on outer circumferential surfaces of a plurality of rollers, respectively. In this type of background sheet feeding device, a contracting force is produced in the direction of the belt's width due to the tension caused by the rollers and exerted in an extending direction of the conveyor belt. Then, a reaction force against the contracting force is exerted in the outer circumferential direction of the conveyor belt. Consequently, as illustrated in FIG. 1, a circular portion 802 of a conveyor belt 801, where a line of convex portions are provided on an inner circumferential surface of the conveyor belt 801, may be protruded toward its outer circumferential surface side. As a result, flatness of the outer circumferential surface of the conveyor belt 801 is impaired, resulting in a sheet conveyance failure such as a sheet skew. If such a sheet conveyance failure occurs at an image reading position, an image of the original document cannot be properly read by the image reading device, resulting in deterioration of image quality. In FIG. 1, the conveyor belt 801 is spanned around a drive roller 803, a pressure roller 804, and a driven roller 805.
Further, in another background sheet feeding device, convex portions each having a trapezoid shape are fixed on an inner circumferential surface of the conveyor belt to avoid shifting. The conveyor belt is spanned around a plurality of rollers, and the convex portions of the conveyor belt engage a timing pulley formed on an end portion of each of the rollers. In this background sheet feeding device, because a plurality of grooves of the timing pulley have uniform intervals, the convex portions of the conveyor belt need to be attached to the timing pulleys of the rollers accurately, thus also requiring a high degree of accuracy in the processing of parts, which results on an increase of the overall cost of the device.
In the above-described background sheet feeding device in which the convex portions of the conveyor belt engage in the concave portions of the rollers, the concave portions of the rollers need to be in proper alignment with each other in the sheet conveying direction to securely engage with the convex portions of the conveyor belt. If the concave portions of the rollers are not aligned properly in the sheet conveying direction, the convex portions of the conveyor belt may disengage from the concave portions of the rollers and go on the outer circumferential surfaces of the rollers as the conveyor belt rotates, thereby causing the conveyor belt to shift in the direction perpendicular to the sheet conveying direction. As a result, the conveyor belt cannot convey a sheet stably. Practically, it is difficult to align the concave portions of the rollers in the sheet conveying direction of the conveyor belt due to variations in accuracy of parts and attachments.